Automatic shut-off valve for power tools

ABSTRACT

A fluid-actuated shut-off valve for a fluid-powered tool such as a wrench including a spool valve urged to open position by a spring and having respective valve-operating surfaces subject to both regulated inlet and exhaust pressures in the tool. The valve operating surfaces and spring are arranged so the valve is thrown to its closed position by a combination of a constant regulated control pressure and the drop in exhaust pressure as the tool motor slows down and stalls under load.

BACKGROUND OF THE INVENTION

This invention relates to power tools and more particularly to afluid-actuated shut-off valve for a fluid-powered tool such as a wrench.

U.S. Pat. No. 3,656,560, issued Apr. 18, 1972, to R. J. Catterfeld, etal, discloses a prior art fluid-actuated shut-off valve for afluid-powered tool. The prior art tool worked well for any given inletpressure. However, wide variations in inlet pressure could not betolerated without tool adjustment.

SUMMARY OF THE INVENTION

A principal object of this invention is to provide a novelfluid-actuated valve mechanism of the foregoing type which substantiallyeliminates or minimizes the disadvantages of the prior art.

Other important objects of this invention are: to provide a novelshut-off valve actuated by fluid and responsive to the torque load on atool; to provide a shut-off valve that operates without a restriction inthe fluid inlet passage of the tool; and to provide a tool shut-offvalve of a simplified and economical construction which incorporates ameans for regulating control pressure so as to afford a wider range ofacceptable inlet pressure and, therefore, torque output variance withouttool adjustment and while retaining reliable shutoff upon achievingstall torque.

In general, the foregoing objects are attained in a tool constructionincluding a fluid motor, a fluid inlet passageway and a fluid exhaustpassageway, a fluid-operated valve located in the inlet passageway andmovable between alternate positions including an open position allowingmotive fluid to flow to the motor and a closed position preventingmotive fluid from flowing to the motor, spring means urging the valve toits open position, first valve-operating means subject to a regulatedpressure and time rise rate of pressure and urging the valve to itsclosed position, second valve-operating means subject to pressure in theexhaust passageway and urging the valve to its open position with thespring means, the first and second valve-operating means being arrangedso that the valve will move to its closed position in response to thedrop in fluid pressure in the exhaust passageway when the motor slowsdown and stalls under a load.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described in connection with the accompanying drawingwherein:

FIG. 1 is an elevational view with portions shown in section of a powertool containing the shut-off valve of this invention and showing thevalve in its open position; and

FIG. 2 is a fragmentary view of FIG. 1 showing the valve spool inelevation and in the closed position.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 shows the rear portion of a power wrench casing 1. The casing 1includes a hose fitting 2 at its rear end adapted to connect to an airhose (not shown) and opening into a supply or inlet passageway 4. Theinlet passageway 4 contains a conventional lever-type throttle valve 5operated by a throttle lever 6 engaging a plunger 7 which in turnengages a ball seal 3. The throttle valve 5 is urged shut by a spring 8.

The casing 1 contains a conventional vane-type rotary motor 10 includinga rotor 11 mounted in a rear bearing 12 and rotating in a fixed cylinder13. The rotor 11 also engages a rear end plate 14. The motor includes aninlet 15 connected to the inlet passageway 4 and an exhaust passageway16.

A novel shut-off valve mechanism is mounted in the casing 1 in the inletpassageway 4 intermediate the throttle valve 5 and the motor 10. Thisvalve mechanism includes a closed-end housing or sleeve 18 mounted in acorresponding opening provided in the casing 1 and extending across theinlet passageway 4. The valve sleeve 18 is locked in place in the casing1 by a roll pin 19. The sleeve 18 contains a cylindrical bore 20slidably containing a spool valve 21 and having respective inlet andoutlet ports 22 and 23 communicating with the passageway 4.

The spool valve 21 is shaped and arranged so that it opens thepassageway 4 when in the left position as shown in FIG. 1 and blocks thepassageway 4 when in the right position shown in FIG. 2. The left end 24of the valve 21 contains a cavity which cooperates with the top end 25of the valve sleeve 18 to form a chamber 26. A short passage 27 extendsfrom the passageway 4 on the supply side of the valve 21 to a portopening into the cylindrical bore 20 a short distance from the sleeveend 25 where it is covered by the valve 21 in its open position as shownin FIG. 1. A clearance is provided between the valve 21 and thecylindrical bore 20 sufficient for fluid pressure to flow into thechamber 26 from the inlet passageway 4 in a restricted manner. Fluidpressure in the chamber 26 urges the valve 21 towards its closedposition.

The sleeve end 25 is provided with three passageways leading toatmosphere. The signal port 40 is shown with a seal cap 41 in thepreferred embodiment. The seal cap 41 may be removed, and the signalport utilized to measure pressure for any purpose desired; for example,controlled pressure check or operation of a bolt marking device. Apressure regulating device is installed in pressure regulatingpassageway 42. The pressure regulating means provided in the passagewayconsists of a ball regulator 43 which is held against a regulator valveseat 44 by means of a spring 45, and adjustable end cap 46 which isthreadingly engaged in pressure regulating passageway 42. The adjustableend cap is provided with a vent hole 47 to allow the pressure fluidbypassing valve seat 44 to escape to atmosphere. Adjustable ventpassageway 48 is also provided in the sleeve end 25, and flow throughthe adjustable passageway is controlled by means of a threaded metervalve 49.

It may be appreciated by one skilled in the art, therefore, that thepressure in chamber 26 may be controlled by the spring force setting onball regulator 43. A higher pressure in chamber 26 may be obtained byrotating adjustable end cap 46 to further compress spring 45. A lowerpressure in chamber 26 may be obtained by screwing adjustable end cap 46out so as to relieve the spring force on ball regulator 43. In general,the function of the pressure regulating device is to limit the maximumobtainable pressure in chamber 26.

For the shut-off valve to function properly, it should be understoodthat the rate of rise of pressure in chamber 26 must also be controlled.Manufacturing tolerances without greater expense do not allow for thedegree of control of radial clearance between the spool valve 21 and itsbore 20 to adequately control the rate of pressure rise over a widerange of inlet pressures. The adjustable vent passageway 48 has beenprovided in the present novel combination to accommodate the valve so asto control the pressure rate of rise in chamber 26. This is anespecially important consideration in the prevention of prematureshut-off which can occur during starting of the motor and until the timethe motor has achieved running speed. If the pressure is allowed tobuild up in chamber 26 too rapidly, the balancing force in chamber 31may be insufficient to prevent the spool valve 21 from shifting to itsclosed position. The pressure in chamber 31 is dependent on the exhaustpressure which is "0" at the start of the tool, but builds up quiterapidly as the tool accelerates.

The bottom end 29 of the valve 21 contains a cavity which cooperateswith the casing 1 to form a chamber 31, and a spring 32 is disposed inthe chamber 31 between the casing and the valve 21 to urge the valve 21toward its open position. A conduit 33 interconnects the chamber 31 withthe exhaust passageway 16 whereby fluid pressure from the exhaust in thechamber 31 urges the valve 21 toward its open position.

OPERATION

In describing the operation of the shut-off valve, we assume that, atthe start, the throttle valve is closed, air pressure is in the supplyhose 3, the shut-off valve 21 is in its open position as shown in FIG. 1and the motor 11 is not operating.

The opening of the throttle valve 5 will allow air pressure to quicklystart the motor 11. We will assume that the tool is a power wrench, suchas an angle wrench, driving a nut as the motor starts. The pressure willrise in the exhaust passageway 16 and in the chamber 31 to urge thevalve 21 toward the open position. Also, pressure will flow into thechamber 26 from the inlet passageway 4 through the clearance provided tourge the valve 21 toward its closed position. As previously explained,the function of the pressure regulating device and the adjustable ventserve to control the maximum pressure in chamber 26 and its rate ofrise. By controlling the maximum pressure achieved in chamber 26 bymeans of the ball regulator 43, wider ranges of inlet pressure may betolerated by the shut-off valve mechanism. The exhaust pressure atshut-off is relatively unaffected by the inlet pressure for a normal airmotor. By venting a portion of the air reaching chamber 26 throughadjustable vent passage 48, it may be appreciated that the rate of riseof pressure may thereby be controlled. A slower rate of rise is achievedby venting a greater portion of the pressure fluid through meter valve49. Utilizing the novel combination of the pressure regulation andchamber venting, it is possible to have a reliable shut-off over a widerange of inlet pressure adjustment. The problem of premature shut-offmay be eliminated by this combination without undue tolerances controlbetween the valve 21 and its bore 20. While the motor operates, thepressure in the inlet passageway 4 is substantially less than supplypressure due to the motor 11 using a large volume of air. Also, theexhaust pressure in the exhaust passageway 16 is relatively high due tothe flow of large air volumes through the motor 11.

As the nut driven by the wrench is tightened, the torque load on themotor rises and eventually the motor stalls. As the motor slows down andcomes to a stop, its consumption of air is reduced. The air pressure inthe valve operating chamber 26 remains relatively constant by thepressure regulator. Also, as the air flow through the motor is reduced,the exhaust pressure in the valve-operating chamber 31 is reduced.

Eventually, the differential forces on the valve spool 21 are shifted tomove the valve toward its closed position. As the valve 21 approachesits closed position, as shown in FIG. 2, it uncovers the short passage27 to allow the air to flow freely from the inlet passageway 4 into thechamber 26. This overcomes the ability of the pressure regulator toregulate the pressure in chamber 26, and there is a rapid pressure risewhich assists the valve 21 to its closed position.

The valve 21 will remain in its closed position as shown in FIG. 2,stopping the motor 11 so long as the throttle valve 5 remains open. Whenthe throttle valve 5 is returned to its closed position, the pressure inthe chamber 26 rapidly leaks away due to leakage past the adjustablevent passage 48. As the pressure in the chamber 26 falls, the valve 21is returned to its open position by its spring 32 where it is ready foranother operating cycle.

It has also been found that the response time of the shut-off valve maybe significantly improved by providing a vent 50 for chamber 31. Thisvent prevents a cushion of air from being trapped by spool valve 21 asit moves towards the closed position by the differential pressure atshut-off.

While only a single embodiment of the invention is illustrated anddescribed in detail, this invention is not limited merely to thisembodiment, but contemplates other embodiments and variations whichutilize the concepts and teachings of this invention.

We claim:
 1. A fluid-driven power tool including:a casing containing amotor, an inlet passageway for feeding motive fluid to said motor and anexhaust passageway for exhausting fluid from said motor; afluid-actuated valve located in said inlet passageway and movablebetween alternate positions including an open position allowing motivefluid to flow to said motor and a closed position preventing motivefluid from flowing to said motor; first valve-operating means includingmeans for establishing relatively constant pressure and means foradjustably controlling the rate of pressure rise urging said valve toits closed position; second valve-operating means communicating withsaid exhaust passageway and operative, when subject to fluid pressure,to urge said valve to its open position against the force of said firstvalve-operating means; and said first and second valve-operating meansbeing arranged so that said valve will move to its closed position inresponse to the drop in fluid pressure in said exhaust passageway whensaid motor slows down.
 2. The fluid-driven power tool of claim 1wherein:said means for establishing a relatively constant pressure insaid first valve operating means comprises an adjustable spring pressureregulator.
 3. The fluid-driven power tool of claim 2 wherein:saidpressure regulator comprises a spring loaded ball and cooperatingannular seat.
 4. The fluid-driven power tool of claim 1 wherein:saidmeans for controlling the rate of pressure rise further comprises anadjustable vent.
 5. The fluid-driven power tool of claim 1 wherein:apressure fluid vent is provided on the second valve operating means ofsaid fluid actuated valve to improve its response time to a closedposition.